This application is based on Japanese Patent Application No. 2001-77395 filed on Mar. 19, 2001 the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an apparatus and method for controlling an internal combustion engine (engine).
2. Description of Related Art
It is proposed that a vehicular engine control system using an electronic controller which executes a torque demand control for setting an improved drivability having a quick response to an operation of an accelerator pedal by a driver of the vehicle. In this control method, the controller determines a desired accelerating power or target output torque demanded by the driver based on an operating degree of the accelerator pedal, an engine speed and the like. Then the controller determines operation degree of actuators, such as an opening degree of a throttle valve, a fuel amount injected from injectors, ignition timing of ignition devices and the like. Specifically, a target output torque may be calculated based on the operating degree of the accelerator pedal and the engine speed. A target indicated torque is calculated to add a loss torque of the engine to the calculated target output torque. Then, the opening degree of the throttle valve, the fuel amount and the ignition timing are determined based on the calculated target indicated torque.
Here, the target output torque Tot is a desired value or a target value of a net torque that is obtained on a crankshaft. The target indicated torque Tit is a desired value or a target value of a combustion torque generated by combustions of the engine. The loss torque Tl includes an internal less such as a friction loss in the engine and a torque lost by accessories such as an oil pump, an alternator and the like. A relationship among the values can be expressed by the following expression: Tit=Tot+Tl.
It is important in an idling condition of the engine to maintain the engine speed in a constant manner even if an external disturbance is applied to the engine. However, the conventional torque demand control doesn""t consider a stability of the engine speed in the idling. Hereinafter, the engine speed in the idling is referred to as an idling speed.
Therefore, it is an object of the present invention to provide an apparatus for controlling the internal combustion engine that executes the torque demand control adapted to the idling.
It is a further object of the present invention to provide an apparatus for controlling the internal combustion engine which is capable of stabilizing the idling speed even if the external disturbance is applied.
It is a still further object of the present invention to provide an apparatus for controlling the internal combustion engine which is capable of stabilizing the idling speed even if a feedback control of the idling speed is not executed.
It is another object of the present invention to provide a method for controlling the internal combustion engine that is adapted to the idling.
It is a still another object of the present invention to provide a method for controlling the internal combustion engine which is capable of keeping a stability of the idling speed even if the external disturbance is applied.
It is a yet another object of the present invention to provide a method for controlling the internal combustion engine which is capable of keeping a stability of the idling speed even if a feedback control of the idling speed is not executed.
According to the present invention, at least one of actuators which are capable of varying output of the engine is controlled in accordance with a target indicated power that is substantially constant when the engine is in an idling. In the idling of the engine, an operator of the engine, e.g. a driver, doesn""t operate an accelerator. Therefore, the engine is controlled based on a constant target indicated power. In case of maintaining the target indicated power constant, the output torque of the engine increase as the engine speed decreases. Therefore, if the engine speed increases while the idling, the output torque decreases to decrease the engine speed. That is, according to the present invention, a self-stabilizing method for controlling the engine speed is provided.
An idling speed control may be combined so that an idling speed control with a feedback control method maintains the engine speed at a target engine speed. The self-feedback provided by the constant target indicated power stabilizes the engine speed when the idling speed control with the feedback control method is inhibited.
The target indicated power may correspond to or slightly overcome a loss torque including internal and external losses when the engine is in the idling.
The engine may be controlled in accordance with a target indicated torque when a vehicle driven by the engine is in a driving condition. In the driving condition, the target indicated torque is set based on a target output torque reflecting the operating degree of an accelerator and a loss torque including internal and external losses when a vehicle driven by the engine is in a driving condition.